Siloxane lubricants



Patented June 10, 1952 UNITED STATES SILOXANE LUBRICANTS Maurice C..Hommel, Bay City, Mich., assignor to Dow Corning Corporation, Midland, Mich., a

corporation. of Michigan PATENT OFFICE No Drawing. Application January 25, 1950, Serial No. 140,545

1 Claim. 1

This invention relates to a method of lubricating moving metallic parts and to the lubricants used therein.

The thermal stability and chemical inertness of polysiloxanes make them useful as lubricants under extreme temperature conditions. However, for use under normal operating conditions with ferrous surfaces, the siloxanes. do not compare favorably as lubricants with hydrocarbon oils. Consequently, for normal temperature ranges the use of siloxane lubricants is not usually recommended.

It is disclosed in the copending application of Herbert J. Fletcher et al., Serial No. 115,783, filed September 14, 1949, that improved lubrication with siloxanes is obtained when chlorinated arylpolysiloxanes are employed. Whereas this invention represents a great advancement in the lubricating art, the resulting products are still not within. the same class as hydrocarbon oils for use at normal temperatures.

It is an object of this invention. to provide polysiloxane lubricants which approach the excellence of hydrocarbon oils as to lubricity. Another object is to provide a polysiloxane lubricant which may be employed at high pressures andat extremes of temperature.

The applicant has found that a combination of chlorinated arylpolysiloxanes and a limited number of chlorinated biphenyls and organic sulfldes produce lubricants which, insofar as is known, are greatly superior to any polysiloxane lubricant heretofore employed.

This invention relates to a lubricant composed of halogenated arylpolysiloxanes, from 2 per cent to 10 per cent by weight, based upon the weight of the mixture of a compound of the group chlorinated biphenyls containing from 48 per cent to 68 per cent by weight chlorine and chlornaphthaxanthate containing 31 per cent by weight chlorine and 11 per cent by weight sulfur, and from to 2 per cent by weight, based upon the weight of the mixture of asulfide of the group benzyl bisulfide and 2,benzylthiazyl,N,N-diethylthiocarbamyl. sulfide.

When a film of the lubricants above defined is maintained between the surfaces of moving metallic parts, excellent lubrication as shown by small wearv underloadis obtained.

The polysiloxanes employed herein are constructed of units of the type RSiO3 z, RzSiO; and RJcSiO, so proportioned that the degree of substitution is greater than 2 and less than 3 organic radicals per silicon atom. The R groups are halogenated aryl, methyl, and phenyl groups. However, in all cases the proportion of halogenated aryl radicals is such that the ratio of siloxane halogen to silicon atoms is from 0.05 to 3. In the polysiloxane the halogen atoms are chlorine and bromine, and at least 37 per cent of the total number of organic radicals are methyl radicals.

In the siloxanes of this invention all of the halogen atoms are contained in silicon-bonded halogenated aryl radicals. Such radicals contain from 1 to '7 halogen atoms and are of-the formula C6HnX(5-n) and C12HyX9ywhere n has a value from 0 to 4, inclusive, y has a value from 2 to 8, inclusive, and X is bromine or. chlorine. The latter radicals are halogenated xenyl radicals which term is employed herein to designate the radical CsH5CsI-I4. For the purpose of this invention the above-identified halogenated radicals may be substituted on a silicon atom: in an Rsioa/z, R2SiO, or a RaSiO-i siloxane. unit or on the silicon atoms of any combination of these units.

The halogenated arylpolysiloxanes above defined may be prepared by any of several we1lknown methods. Preferably, the method is that of direct halogenation of the corresponding phenyl or xenylsiloxane. This is best accomplished by contacting the siloxane with the halogen in the presence of FeCh as a catalyst. The catalyst is preferably employed in amount of .1 per cent by weight, based on the weight of the siloxane. Alternatively, the corresponding arylchlorosilanes of the type RnSiClA-n may be halogenated in the same manner. These chlorosilanes are then hydrolyzed to the siloxane.

The halogenated arylpolysiloxanes may be copolymerized with methyl and phenylsiloxanes to produce the copolymers employed in this invention by any of the well-known methods for copolymerizing siloxanes.

I The lubricants of this invention are prepared by adding to the above-defined halogenated arylsiloxanes a chlorinated biphenyl containing from 48 to 62 per cent by weight of chlorine or chlornaphthaxanthate containing 31 per cent by weight chlorine and 11 per cent by weight sulfur.

The biphenyls may be either a single compound or a mixture of compounds containing from about 2 to about 7 chlorine atoms per biphenyl molecule. When a mixture is employed, the various halogenated biphenyls are so proportioned that the mixture will have a per cent by weight chlorine within the range above defined.

It has been found further that improved results are often obtained when in addition to the chlorinated biphenyl, up to 2 per cent by weight based upon the weight of the mixture of benzyl bisulfide or 2,benzylthiazyl,N,N-diethylthiocarbamyl sulfide is added to the mixture.

The lubricants of this invention possess a com bination of excellent lubricity under load and relatively small change in viscosity with temperature which render them excellent for use over a temperature range from below 70 F. to above +300 F. This combination of properties is not obtained by adding the chlorinated biphenyl and the sulfur compounds to a nonhalogenated polysiloxane. It has been found that if sufficient amounts of the additive are mixed with a nonhalogenated arylpolysiloxane, good lubricity will result, but the temperature viscosity slope of the resulting mixture is so poor that the material cannot be employed over a wide temperature range. For example, a phenylmethylpolysiloxane to which 20 per cent by weight of a chlorinated biphenyl containing 62 per cent by weight chlorine is added, will perform satisfac torily as a lubricant under load at normal temperatures. However, the material freezes at about 25 F. and hence, is obviously not suitable for low temperature use. By contrast, siloxanes of this invention produce excellent lubricants when only 4 per cent of the same chlorinated biphenyl is added, and these materials are fluid at temperatures below 70 F.

The lubricants of this invention may be employed as oils or the oils may be converted to a grease by adding thereto any of the thickening agents commonly employed to prepare greases. Examples of such thickening agents are lithium salts of fatty acids and alkali metal salts and alkaline earth metal salts of alicyclic substituted fatty acids wherein the fatty acid has a chain length of from 1 to 6 carbon atoms. The relative proportion of the siloxane and the thickening agent is such that there is at least 50 per cent by weight of the liquid polysiloxane present.

' The lubricants used in this invention consist essentially of the ingredients shown above. Howby means of a ratchet wheel.

ever, they may contain small amounts of other additives such as corrosion inhibitors and other materials which are normally included in lubricants. These minor additives, however, do not affect the main characteristics of the lubricants nor is the effectiveness of the present materials as lubricants dependent thereon.

The superiority of the liquid polysiloxanes of this invention as lubricants was determined by means of a Falex Lubricant Testing Machine. This machine is recognized in the art as giving true measure of the efficiency of a lubricant in preventing wear of the bearing surfaces of moving metallic parts. A description of the machine and its operation is given in an article by Victor A. Ryan in Lubrication Engineering, September 1946, pages 102-104.

Essentially, the test involves rotating a shaft between two V-blocks as pressure is applied to the bearing surfaces. The resulting wear of the shaft and the V-blocks when operated under a given load for a given period of time is measured The wear is expressed in teeth wear, one tooth wear being equal to .0000556 inches of wear in depth.

The results of these tests with lubricants of this invention and a comparison of the instant lubricants with other siloxanes is given in Table I below. These tests were run at room temperature and in all cases a steel shaft and steel V-blocks Were employed.

To better understand this invention, recourse may be had to the following examples which should be considered as illustrative only.

EXAIVLPLE 1 Lubricants were prepared by mixing the siloxanes shown in the table below with the various additives indicated. The siloxanes were agitated until solution of the additive was complete. In cases where the chlorinated biphenyl is quite viscous and/or when the sulfides are employed it is often desirable to warm the mixture in order to facilitate solution of the additive.

A comparison of the lubricity of various siloxanes with and without the additives was made by means of a Falex Lubricant Testing Machine to determine the wear of the bearing surfaces after 30 minutes under the gage loads indicated. The lubricant was said to fail when the gage load dropped to zero showing a prohibitive amount of wear.

For the sake of comparison, test runs with a common petroleum oil are included.

Table I Composition of siloxane Per cent chlorinated biphenyl Per cent sulfide as weight Initial Teeth in mol per cent as weight per cent of mixture per cent of mixture 3 58 13 3 gg g gf None None 2o Failed 5OCuH5(CH3 )S10, 35(CH3)2S10, 50 150 15(OH3)3S1O; 4% containing 62% chlorine... None 100 186 22g Failed 153 sonolnasio sswnolsio, 100 234 I 100 50 l- 4% containing 62% chlorine- None 200 49 300 165 None None 3g g D 100 16 so nlohsio (CH3);SiO, 4% mammg 62% 10(0119351034 2% containing 62% chlorine 1% Benzyl bisulflde g 4% containing 62% chlorine. 0.1% 2benzylthiazyl, N,N 8 V giiethyl thiocarbamyl sul- 200 3 e. t 100 5 Pesgiigeigion Q11 Quaker State N None 200 4 EXAMPLE 2 Excellent lubricity, as shown by low wear, is obtained when a lubricant having the following composition is employed to lubricate the bearing surfaces of moving metallic parts:

5B12C6H3SiO3/2, 80(CH3)2S1O. 5(CsI-Is) 2Si0,

CsH5(CH3)2SiO1 2 and 6 per cent by weight based upon the weight of the mixture of a chlorinated biphenyl containing 48 per cent by weight chlorine.

EXAMPLE 3 100 grams of a liquid copolymeric siloxane having the composition 10 mol per cent 81.5 mol per cent (CHaMSiO and 8.5 mol per cent (CH3)3siO1/2 was mixed with 10 grams of a v.chlornaphthaxanthate containing 31 per cent by weight chlorine and 11 per cent by weight sulfur and having a sp. gr.

minutes under a gage load of 200 pounds.

That which is claimed is:

A lubricant composed of a halogenated arylpolysiloxane fluid, from 2 per cent to 10 per cent by weight, based upon the weight of the mixture of a compound selected from the group 6 consisting of chlorinated biphenyls containing from 48 per cent to 62 per cent by weight chlorine and chlornaphthaxanthate containing 31 per cent chlorine and 11 per cent sulfur, and from 0 to 2 per cent by weight based upon the weight of the mixture of a sulfide selected from the group consisting of benzyl bisulfide and 2,benzylthiacyl,N,N diethylthiocarbamyl sulfide, said halogenated arylpolysiloxane havinga degree of substitution greater than 2 and less than 3 organic radicals per silicon atom, said siloxane containing halogenated aryl radicals selected from the group consisting of halogenated phenyl and halogenated xenyl radicals having substituted therein from 1 to 7, inclusive, halogen atoms selected from the group consisting of chlorine and bromine, the remaining organic radicals in said siloxane being selected from the group consisting of methyl and phenyl radicals in which siloxane the halogenated aryl radicals are present in amount so that the ratio of halogen atoms to silicon atoms is from 0.05 to 3 and in which siloxane at least 3'? per cent of the total number of organic radicals are methyl radicals.

MAURICE C. HOMMEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

